Oxidative dehydrogenation of olefins with an antimony oxide-cerium oxide catalyst



United States Patent OXIDATIVE DEHYDIQOGENATION 0F OLEFINS WITH ANANTIMONY OXIDE-CERIUM OXIDE CATALYST James L. Callahan, Bedford, Ohio,Berthold Gertisser, New York, N.Y., and Robert Grasselli, Cleveland,Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, acorporation of Ohio No Drawing. Filed Oct. 15, 1962, Ser. No. 230,742

6 Claims. (Cl. 260-680) This invention relates to the catalyticoxidative dehydrogenation of olefins to diolefins, such as butene-l tobutadiene, and tertiary amylenes to isoprene, using an improvedoxidation catalyst consisting essentially of oxides of the elementsantimony and cerium.

US. Patent No. 2,904,580 dated September 15, 1959, describes a catalystcomposed of antimony oxide and molybdenum oxide, as antimony molybdate,and indicates its utility in converting propylene to acrylonitrile.

British Patent 864,666 published April 6, 1961, describes a catalystcomposed of an antimony oxide alone or in combination with a molybdenumoxide, a tungsten oxide, a tellurium oxide, a copper oxide, a titaniumoxide, or a cobalt oxide. These catalysts are said to be either mixtures of these oxides or oxygen-containing compounds of antimony withthe other metal, such as antimony molybdate or molybdenum antimonate.These catalyst systems are said to be useful in the production ofunsaturated aldehydes such as acrolein or methacrolein from olefins suchas propylene or isobutene and oxygen.

British Patent 876,446 published August 30, 1961, describes catalystsincluding antimony, oxygen, and tin, and said to be either mixtures ofantimony oxides with tin oxides, or oxygen-containing compounds ofantimony and tin such as tin antimonate. These catalysts are said to beuseful in the production of unsaturated aliphatic nitriles such asacrylonitrile from olefins such as propylene, oxygen and ammonia.

I. THE CATALYST.

In accordance with the invention, an oxidation catalyst is providedconsisting essentially of oxides of antimony and cerium. This catalystis useful not only in the oxidation of olefins to oxygenatedhydrocarbons such as acrolein and the oxidation of olefin-ammoniamixtures to unsaturated nitriles such as acrylonitrile, but also in thecatalytic oxidative dehydrogenation of olefins to diolefins.

The nature of the chemical compounds which compose the catalyst of theinvention is not known. The catalyst may be a mixture of antimony oxideor oxides and cerium oxide or oxides. It is also possible that theantimony and cerium are combined with the oxygen to form an'antimonate.X-ray examination of the catalyst system has indicated the presence of astructurally common phase of the antimony type, composed of antimonyoxides, and some form of cerium oxide. Antimony tetroxide has beenidentified as present. For the purposes of description of the invention,this catalyst-system will be referred to as a mixture of antimony and,cerium oxides, but this is not to be construed as meaning that thecatalyst is composed either in whole or in part of these compounds.

The proportions of antimony and cerium in thecatalyst system may varywidely. The SbzCe atomic ratio can range from about 1:50 to about 99:1.However, optimum activity appears to be obtained at SbzCe atomic ratioswithin the range from 1:1 to 25: 1.

The catalyst can be employed without support, and will display excellentactivity. It also can be combined with a support, and preferably atleast 10% up to about 90% of the supporting compound by weight of theentire composition is employed in this event. Any known supportmaterials can be used, such as, for example, silica, alumina, zirconia,alundum, silicon carbide, aluminasilica, and the inorganic phosphates,silicates, aluminates, borates and carbonates stable under the reactionconditions to be encountered in the use of the catalyst.

The antimony oxide and cerium oxide can be blended together, or can beformed separately and then blended, or formed separately or together insitu. As starting materials for the antimony oxide component, forexample, there can be used any antimony oxide, such as antimonytrioxide, antimony tetroxide and antimony pentoxide, or mixturesthereof, or a hydrous antimony oxide, metaantimonic acid, orthoantimonicacid or pyroantimonic acid; or a hydrolyzable or decomposable antimonysalt, such as an antimony halide, for example, antimony trichloride,trifluoride or triobromide; antimony pentachloride and antimonypentafluoride, which is hydrolyzable in water to form the hydrous oxide.Antimony metal can be employed, the hydrous oxide being formed byoxidizing the metal with an oxidizing acid such as nitric acid.

The cerium oxide components can be provided in the form of cerous oxide,ceric oxide, or ceric peroxide, or by precipitation in situ from asoluble cerium salt such as the nitrate, acetate, or a halide such asthe chloride. Metallic cerium can be used as a starting material, and ifantimony metal is also employed, the antimony can be converted to theoxide and the cerium to the nitrate simultaneously by oxidation in hotnitric acid. A slurry of hydrous antimony oxide in nitric acid can becombined with a solution of a cerium salt such as diammonium cericnitrate, which is then precipitated situ as the hydroxide by making thesolution alkaline with ammonium hydroxide, the ammonium nitrate and theother ammonium salts being removed by filtration of the resultingslurry.

It will be apparent from the above that cerous carbonate, cerousbromide, cerous bromate, cerous chloride, cerous fluoride, cerousiodide, cerous molybdate, ceric hydroxy nitrate, cerous acetate, ceroussulfate, ceric sulfate, cerous phosphate, ceric hydroxide, cerousformate and cerous hydroxide can be employed as the source of the ceriumoxide component.

The catalytic activity of the system is enhanced by heating at anelevated temperature. Preferably, the catalyst mixture is dried andheated at a temperature of from about 500 to about 1150 F., preferablyat about 700 to 900 F., for from two to twenty-four hours. If activitythen is not sufi'icient, the catalyst can be further heated at atemperature above about 1000 F., but below a temperature deleterious tothe catalyst at which it is melted or decomposed, preferably from about1400 F. to about 1900 F. for from one to forty-eight hours, in thepresence or air or oxygen. Usually, this limit is not reached before2000 F. and in some cases this temperature can be exceeded.

In general, the higher the activation temperature, the less timerequired to effect activation. The sufiiciency of activation at anygiven set of conditions is ascertainedby a spot test of a sample of thematerial for catalytic activity. Activation is best carried out in anopen chamber, permitting circulation of air or oxygen, so that anyoxygen consumed can be replaced.

The antimony oxide-cerium oxide catalyst composition of the inventioncan be defined by the following empirical formula:

Sb valence may range from 3 to 5 and the Ce valence from 3 to 4. e

, tial.

II. THE OXIDATIVE DEHYDROGENATION OF OLEFINS TO DIOLEFINS AND AROMATICSIn accordance with the present invention, this catalyst system isemployed in the catalytic oxidative dehydro genation of olefins todiolefins and aromatics. In this process, the feed stream in vapor formcontaining the olefin to be dehydrogenated and oxygen is conducted overthe catalyst at a comparatively low temperature to obtain thecorresponding diolefin or aromatic compound.

By the term olefin as used herein is meant the open chain as Well ascyclic olefins. The olefins dehydrogenated in accordance with theinvention have at least four and up to about eight nonquaternary carbonatoms, of which at least four are arranged in series in a straight chainor ring. The olefins preferably are either normal straight chain ortertiary olefins. Both cis and trans isomers, where they exist, can bedehydrogenated.

Among the many olefinic compounds which can dehydrogenated in this wayare butene-l; butane-2; pentene-l; pentene-2; tertiary pentenes andhexenes having one tertiary carbon atom such as 2-methyl-pentene-l, 3-methylbutene-l and 2-methylbutene-2, hexene-l, hexene-2,4-methyl-pentene-1, 3,4-dimethyl-pentene-1, 4- methyl-pentene-2,heptene1, octene-l, cyclopentene, cyclohexene, 3-methyl cyclohexene, andcycloheptene.

Open chain olefins yield diolefins, and in general, sixmembered ringolefins yield aromatic ring compounds. The higher molecular weight openchain olefins may cyclize to aromatic ring compounds.

The feed stock in addition to the olefin and oxygen can contain one ormore paraflinic or naphthenic hydrocarbons having up to about carbonatoms, which may be present as impurities in some petroleum hydrocarbonstocks and which may also be dehydrogenated in some cases. Propylene andisobutylene should not be included in substantial amounts.

The amount of oxygen should be within the range from 0.3 to about 3moles per mole of olefin; Stoichiometrically, 0.5 to 1.5 moles of oxygenper mole of olefin is required for the dehydrogenation to diolefins andaromatics, respectively It is preferred to employ an excess, from 1 toabout 2 moles per mole of olefin, in order to ensure a higher yield ofdiolefin per pass. The oxygen can be supplied as pure or substantiallypure oxygen or as air or in the form of hydrogen peroxide.

When pure oxygen is used, it may be desirable to incorporate a diluentin the mixture, such as steam, carbon dioxide, or nitrogen.

The feed stock is preferably catalytically dehydrogenated in thepresence of steam, but this is not essen- Usually, from about 0.1 toabout 6 moles of steam per mole of olefin reactant is employed, butamounts larger than this can be used.

The dehydrogenation proceeds at temperatures within the range from about325 C. to about 1000 C. Optimum yields are obtainable at temperaturesWithin the range from about 400 to about 550 C. However, since thereaction is exothermic, temperatures in excess of 550 C. should not beused, unless means is provided to carry olf the heat liberated in thecourse of the reaction. Due to the exothermic nature of the reaction,the temperature of the gaseous reaction mixture will be higher than thetemperature of the feed entering the system by as much as 75 C. Thetemperatures referred to are those of the entering gas feed near thereactor 50 seconds but higher contact times can be used if de-'comparatively small reactors and small amounts of cata-.

lyst can be used eifectively.

The catalyst can be supplied in the form of tablets or pellets suitablefor use in a fixed bed, with or without a support, maintained at thereaction temperature, passing the feed vaporsthrough the bed. In thismethod of operation, the partial pressure of oxygen is high at the inletand low at the outlet. The concentration of diolefin, on the other hand,is substantially zero at the inlet and at a maximum at the outlet.

The catalyst can also be provided in the form of a fluidized bedemploying the catalyst in powdered form.

The reactor may be brought to the reaction temperature before or afterthe introduction of the vapors to be reacted. In a large scaleoperation, it is preferred to carry out the process in a continuousmanner and in this system the recirculation of unreacted olefin and/oroxygen is contemplated. Periodic regeneration or reactivation of thecatalyst is also contemplated. This may be accomplished, for example, bycontacting the catalyst with air at an elevated temperature.

The efiiuent from the reaction zone can be quenched, but normally thisis not required, inasmuch as there is little tendency for side reactionsto take place, particularly at the preferred temperature range. Theeflluent can then be washed with dilute caustic to neutralize any acidspresent, and remove the steam. IfIair isused as a source of oxygen theetlluent is then compressed and scrubbed with oil to separate thehydrocarbons from the nitrogen, carbon dioxide and carbon monoxide. Thehydrocarbons may then be stripped from the oil, and subjected to anextractive distillation or a copper ammonia acetate treatment toseparate and recover the diolefin. Unreacted olefin can be recycled tothe reactor.

The following example, in the opinion of the inventors, representspreferred embodiments of the process of oxidative dehydrogenation ofolefins in accordance with the invention.

Example The following procedure was employed to prepare a catalysthavingan Sb/Ce atomic ratio of 10.4:1.

to 190 cc. of concentrated nitric acid, specific gravity 1.42, and themixture boiled until all red oxides of nitrogen had been given otf. Tothis was added anaqueous solution of 19.6 g. of diammonium cericnitrate. slurrywas diluted with approximately 150 cc. of 28% ammoniumhydroxide. The slurry was filtered, and the filter cake washed with 300cc., divided into three portions, of 2.5% ammonium hydroxide solution.Air was drawn through the filter cake for 15 minutes following the lastwashing. The catalyst was dried for 3 to 4 hours at' C., calcined at 800F. for 12 hours, and activated by heating for 14 hours at 1400 F. in amuffle furnace open to the atmosphere.

The activity of this catalyst in the oxidative dehydrogenation ofbutene-l to butadiene was determined using a micro-scale reactor havinga capacity of approximately 5 m1. of catalyst charge in a fixed bed. Thefeed gases were metered by Rotameters. In the tests, a 5 ml. catalystcharge was used. The feed ratio butene-l/air was 1/6. The contact timewas 5 seconds, and the temperature was maintained at 880 F. atatmospheric pressure. Of the butene-l ,fed, 26.6% was converted tobutadiene in a single pass.

45 g. of antimony metal (less than 270 mesh) was added slowly The t Weclaim:

1. The process for the oxidative dehydrogenation of olefins to diolefinswhich comprises contacting a mixture of oxygen and an olefin having atleast four up to about eight nonquaternary carbon atoms, of which atleast four are arranged in a series, in the vapor phase at a temperatureat which the oxidative dehydrogenation proceeds with a catalystconsisting essentially of an active catalytic oxide complex of antimonyand cerium, the SbzCe atomic ratio 7 being within the range from about1:50 to about 99:1,

said complex being formed by heating the mixed oxides of antimony andcerium in the presence of oxygen at an elevated temperature of above 500F. but below their melting point for a time suficient to form saidactive catalytic oxide complex of antimony and cerium.

2. The process in accordance with claim 1, wherein the catalyst has anSbzCe atomic ratio of from 1:1 to 25: 1.

3. The process in accordance with claim 1, in which the reaction iscarried out at a temperature within the range from about 325 to about1000 C.

4. The process in accordance with claim 1, in which the olefin has fromabout four to about eight carbon atoms in a straight chain.

5. The process in accordance with claim 1, in which the proportion ofoxygen in the feed is maintained at from 0.3 to 3 moles per mole ofolefin.

6. The process in accordance with claim 1, wherein the olefin is abuteue.

References Cited by the Examiner UNITED STATES PATENTS 2,178,601 11/1939Morrell 260-680 2,326,258 8/1943 Schmidt etal. 260-680 2,383,711 8/1945Clark et a1. 260597 3,094,565 6/1963 Bethell et al 260604 PAUL M.COUGHLAN, Primary' Examiner.

ALPHONSO D. SULLIVAN, Examiner.

1. THE PROCESS FOR THE OXIDATIVE DEHYDROGENATION OF OLEFINS TO DIOEFINSWHICH COMPRISES CONTACTING A MIXTURE OF OXYGEN AND AN OLEFIN HAVING ATLEAST FOUR UP TO ABOUT EIGHT NONQUATERNARY CARBON ATOMS, OF WHICH ATLEAST FOUR ARE ARRANGED IN A SERIES, IN THE VAPOR PHASE AT A TEMPERATUREAT WHICH THE OXIDATIVE DEHYDROGENATION PROCEEDS WITH A CATALYSTCONSISTING ESSENTIALLY OF AN ACTIVE CATALYTIC OXIDE COMPLEX OF ANTIMONYAND CERIUM, THE SB:CE ATOMIC RATIO BEING WITHIN THE RANGE FROM ABOUT1:50 TO ABOUT 99:1, SAID COMPLEX BEING FORMED BY HEATING THE MIXEDOXIDES OF ANTIMONY AND CERIUM IN THE PRESENCE OF OXYGEN AT AN ELEVATEDTEMPERATURE OF ABOVE 500*F. BUT BELOW THEIR MELTING POINT FOR A TIMESUFFICIENT TO FORM SAID ACTIVE CATALYTIC OXIDE COMPLEX OF ANTIMONY ANDCERIUM.